This invention relates generally to impellers for centrifugal compressors. More particularly, this invention relates to an improved open impeller for a centrifugal compressor that has a plurality of circumferentially spaced vanes located on the rear face of the impeller.
The high rotational speeds now used in centrifugal compressors has resulted in vibration of impeller discs which may reduce the efficiency of the compressor or result in the destruction of the impeller and perhaps the compressor. In an effort to alleviate the vibrational problems, ribs or flutes have been utilized on the face of the impeller between adjacent impeller blades.
Discs having relatively large thickness have also been utilized to overcome the vibration problems. With the thicker disc impellers, greater strength and more costly materials have been required which increase the cost of the compressor. Also, the use of the thicker discs have the side effect of causing shaft and bearing problems due to the high rotational speed of the greater mass.
U.S. Pat. No. 4,277,222, issued July 7, 1981, to Dennis E. Barbean illustrates a relatively thin disc impeller that includes two circumferential rings on the back or rear surface of the impeller. The rings inherently provide more rigidity to the relatively thin disc of the impeller. As patented therein however, the rings are provided as annular seals. The use of rings results in hoop stresses being increased in the hub of the impeller. It should be noted that the use of rings is an improvement over the thicker discs which also cause hoop stress problems in the hub.
An object of this invention is to provide an improved open impeller design wherein the impeller disc can be constructed from relatively thin material and yet avoid vibrational problems by incorporating a plurality of circumferentially spaced vanes on the rear surface of the disc that are located generally between the impeller blades. The use of circumferentially spaced vanes also avoids the introduction of additional hoop stresses into the impeller hub.